What is electrical discharge manufacturing? For more details, continue reading.
Using thermal energy rather than mechanical force to remove material from a workpiece, electrical discharge machining (EDM) is an unconventional method of precision machining. Because it uses electrical sparks that are between 8000 and 12000 degrees Celsius, it is sometimes called “spark machining.” When CNC turning and milling can’t produce the desired cut, such as sharp internal corners or a particularly deep cavity, engineers frequently turn to EDM.
Continue reading for an overview of electrical discharge machining machines, the different kinds of EDM that are available, and which EDM machining method is best for your project.
Table of Contents
How Does the EDM Process Work?
The electrode and the workpiece/material are the two main components of the process. To one end of the power supply, each is connected. The workpiece and the electrode each carry one side of the charge.
Due to the large potential difference between the two, when they are close enough, a white-hot electrical spark jumps from the electrode to the workpiece. In the spark gap, this raises the temperature to between 8,000 and 12,000 degrees Celsius, melting the material and causing it to erode.
Such high temperatures necessitate the use of an insulating or dielectric fluid. Throughout the process, the workpiece and the electrode are submerged in the dielectric fluid.
The electric spark is managed by the dielectric fluid. It also functions as a process coolant and flushes out the minute particles that are eroded during the process.
The eroded particles can be as small as 2 microns. For comparison, the thickness of human hair is 70 microns (+/- 20 microns). The eroded particles are so small that they are similar to dust and smoke particles in size. As a result, EDM enables us to work with high levels of precision.
It is important to note that the entire process is completely automated and CNC controlled. No human involvement. The process for a part can even be generated automatically from models created in 3D CAD programs.
Types of EDM
Three common types of electric discharge machining exist: die sinking EDM, wire EDM, and hole drilling EDM.
Die Sinking EDM
The best Electro Discharge Machining for making parts with intricate cavities is die sinking EDM, also referred to as Ram, sinker, traditional, volume, or cavity-type EDM. Additionally, it is the technique used to address the problem of the sharp internal corner when CNC machining. The workpiece and the electrode are connected by an electric spark in this technique, which also uses a dielectric fluid and graphite or copper electrodes.
An electrode is created in the first step of this procedure in the opposite shape of the necessary cavity. This creates the die, which is then immersed in a dielectric fluid like oil to induce a voltage between it and the electrically conductive workpiece.
As soon as there is an “electric breakdown,” a spark jumps the “spark gap,” and the die is gradually lowered toward the workpiece. This causes material on the workpiece to vaporize and melt, and any ejected particles are then carried away by dielectric fluid. This process frequently results in a small amount of the electrode being eroded.
The desired shape will start to take shape and be precisely cut out as the series of high-frequency sparks repeatedly remove a small amount of material from the workpiece. This die-sinking EDM process can be depicted in the image below:
Every aspect of this process, between the servers, power supply, and position of the electrodes, is completely controlled through precision machining.
Wire EDM
Extrusion dies are frequently made using wire EDM, also referred to as wire erosion. It cuts similarly to die-sinking. The electrode, on the other hand, is now in place of the die and is made of a very fine, electrically charged wire. When using this machining technique, a three-dimensional part is cut in two dimensions, like a cheese cutter.
The wire typically has a diameter of only 0.05 to 0.35 millimeters. To prevent the use of burned wire and to guarantee accurate cutting, a fresh wire is continuously spooled by an automatic machine. The below image illustrates the way wire is utilised in wire EDM:
Extremely precise cuts will be produced by this process. Wire EDM by itself won’t be able to give you truly square corners, though, if you’re looking to cut sharp inside corners. Depending on the wire diameter, the radius produced by the wire and spark gap will be between 0.13mm and 0.15mm, but it may also be smaller or larger.
If that is insufficient for your project, a tiny dogbone corner can be used to produce perfectly square internal corners. Read our guide on how to machine square corners for more information on the best ways to machine sharp internal corners.
In some cases, it is preferable to begin a cut in the middle of a part rather than at one of the edges. An extrusion die’s center, for instance, might be machined into a complex shape. If so, hole drilling EDM can create a tiny hole so the wire can be threaded through it to perform wire EDM machining.
Read about What Is Wire EDM?
Hole Drilling EDM
EDM for hole drilling is used to create holes, as the name suggests. However, compared to conventional hole drilling techniques, this method can accurately machine incredibly small and deep holes that don’t need to be deburred.
The basic tenets of this approach are the same as those of die-sinking EDM. To make the cut, a pulsing cylindrical electrode that is moving deeper into the workpiece while being fed with dielectric fluid into the cutting area is used.
The development of high-temperature turbine blades has depended heavily on this technique because it enables the production of extremely complex cooling channels inside the turbine blades.
Advantages
Compared to conventional machining techniques, electro discharge machining offers a number of benefits. Some of these advantages are unique to EDM while others are found in newer methods such as waterjet and laser cutting. Let us take a look at some of these:
Greater Accuracy
One of the highest accuracy among contemporary manufacturing processes is offered by electrical discharge machining. The accuracy of a standard setup is up to 0.025 mm, but there are specialized EDM machines that can reach 0.005 mm.
A part’s accuracy is influenced by a variety of elements, including the material’s properties, the machining process, and the desired level of surface finish.
Complex Designs
Extremely complex and intricate shapes can be created and manufactured using EDM. Creating these shapes using conventional techniques would be very challenging, if not impossible.
Amazing Surface Finish
EDM cuts are zero-directional and don’t produce any machining marks unless the machining time is slashed below a predetermined limit.
The low rate of material removal is the cause of the high-quality finish. EDM leaves a smooth surface that doesn’t require additional treatment for a satisfactory surface finish because only minute particles are removed at a time.
Wide Range of Workable Materials
EDM is effective with a variety of materials because most metals are good electrical conductors.
Non-contact Process
In the EDM procedure, there is no use of a cutting tool. Consequently, no mechanical pressure or force is applied to the workpiece. Electrical discharge machining allows for the risk-free machining of even incredibly soft materials that would ordinarily be vulnerable to damage or breaking due to the pressure from the cutting tool.
Disadvantages
Every manufacturing process has its restrictions. There are always compromises to be made. The disadvantages of using EDM are as follows:
Electrode Cost
In EDM, the tool electrode life is constrained. The same as the workpiece, it is prone to erosion. As a result, it may become difficult to create features with internal corners that are sharp as the tool’s life wears down.
For dependable parts, it is advised to regularly replace the electrode. Depending on the complexity and replacement rate of the electrodes, the cost has an impact on the process’s viability. To some extent, this cost is offset, though, if there are many manufactured parts.
High Power Consumption
A process that uses a lot of power is EDM. For efficient machining, a high current must flow continuously. To accommodate different EDM applications, the power system and feed would need to be modified.
In order to reduce tool wear, the die sink EDM, for instance, uses a transistorized power system. Since there is less chance of a wire rupturing during wire EDM, a transistor-controlled capacitive power system is used. Due to its higher material removal rate and process stability, a capacitive power system is typically used in hole drilling EDM.
The construction of the machining tool and the machining parameters affect the rate of consumption. When cutting AISI P20 steel, the power ranges between 5 and 8 kW.
Does Not Work With Non-conductive Materials
Poor electrical conductors will prevent the process from working. Common materials like plastic, composites, and glass cannot be machined.
HAZ Formation
Development of the heat affected zone can be a concern but the spread and the effect on the microstructure is far lower than alternative machining methods.
According to research, the material influences how much HAZ develops. But in all circumstances, managing variables like the amount of heat that is available, its conduction, and cooling action can significantly lessen the development of HAZ.
EDM and Safety?
Many technicians who are using EDM for the first time are concerned about its safety. It appears to be a safety risk to inexperienced workers due to the requirement for high voltage and recurring sparks. However, there is little risk if the machine is operated in accordance with the manufacturer’s instructions.
The Metalforming Magazine offers guidance on how to guarantee process security. These are some of the measures that need to be taken to run an EDM machine safely:
- Operators and workers have to be properly trained to work with electrical discharge machining
- Make sure that fire safety precautions are put in place and maintained frequently.
- Monitor the fluid: The dielectric fluid’s level must be kept at a certain level at all times. The liquid stops the discharge from spreading to conductive materials besides the workpiece.
- Gases that may be produced in the fluid as a result of chemical reactions associated with the discharge can be removed from the air by using proper ventilation.
- To make sure the dielectric fluid maintains its non-conductive properties while it is circulated, you must keep an eye on it.
When to Use EDM
Some applications for electro-discharge machining may include:
- Micro-hole drilling
- Cutting sharp internal corners
- Creating injection moulding tools
- Cutting extrusions
- Cutting rotary forms
- Drilling curved holes
- Engraving on hard materials
- Removing broken tools from workpieces
Actionable Design Tips for Your EDM Part
When you need to make an EDM part, there are a few things to keep in mind. The following advice will enable you to lower the price of your EDM component without sacrificing the design.
- When cutting internal corners, wire EDM will leave some radius. Due to the spark gap, this internal corner radius typically exceeds the wire radius slightly. As a result, the maximum wire diameter depends on the value that this corner radius can have. A thicker wire can be used, speeding up the process, with a higher permissible value.
- During an EDM process, there may be some material exchange between the wire and the material. If one is not careful, post-machining cleaning could result in galvanic corrosion.
- The vendor must be able to offer fixtures that enable stacking or multiple EDM operations on a single part to perform similar operations on several parts at once at a lower cost.
- The majority of waste should, if at all possible, be eliminated using conventional techniques, and EDM should only be used for finishing touches. Doing so will cut down on both the overall cost of production and the time required for EDM machining.
- Loosen the part’s surface finish tolerances as far as practical, this reduces the number of passes the manufacturer needs to fabricate the part. Greater current magnitude and faster material removal are made possible by rougher surface finishes.
Summary: What is the Electrical Discharge Machining?
Electrical discharge machining is an excellent method to use in conjunction with a traditional machining method such as CNC machining when parts have specific geometrical requirements. Furthermore, it is a desirable option when working with materials like Inconel due to the process’s capacity to machine hard materials. High-volume tasks, on the other hand, are not well suited for this method because the machining process is relatively slow. Watch this video tutorial for a visual walkthrough of the processes involved within EDM.
